Swimming pool water must undergo treatment in order to remain clear, clean, free from pathogens, and suitable for use by bathers. Swimming pools (also referred to herein as “pools”) chlorinated by the introduction of sodium or calcium hypochlorite contain high levels of dissolved salts in the form of sodium or calcium anions whereas conventional salt chlorinated pools contain high levels of sodium chloride, typically in a recommended concentration of about 6000 ppm.
Apart from very high salt concentrations, pool water can also contain chloramine or trihalomethane (THM) compounds arising from the reaction of free chlorine cations with bodily fluids, skin, and other contaminants in the pool water as well as cyanuric acid chlorine stabilizers and microorganisms such as bacteria, viruses, algae and parasites. The levels of these contaminants are higher in non-residential pools with a large number of bathers which increases the levels of chlorine required to keep these pools clean. This leads to extended periods of “superchlorination”, during which the pool cannot be used. The presence of chloramines and trihalomethanes in swimming pools is harmful to humans since these compounds are the underlying cause of a number of serious health problems including forgetfulness, fatigue, chronic colds, voice problems, eye irritations, headache, sore throat, eczema and frontal sinus inflammation. These toxic compounds are also the precursors of vital health concerns such as asthma, cancer, and reproductive defects, making their presence in pools highly undesirable.
Pools using electrolytic generators typically contain between 3000 and 6000 ppm of sodium chloride (NaCl) as these are the levels required for the electrolytic chlorinators to work efficiently. The presence of such high salt contents in the backwash and rinse water makes it unsuitable for collection and use in garden irrigation because gradual accumulation of sodium chloride in the soil leads to problems such as salinity induced soil degradation.
Furthermore, the fact that many swimming pools contain high levels of phosphates, which act as a primary source of nutrition for algae, has increased the levels of sanitizers required to maintain satisfactory control of algae and adequate water clarity.
As used herein, the expression “swimming pool” is also intended to embrace the analogous use of spa baths, hot tubs and the like which are operated in a substantially identical manner to swimming pools.